Window frames may consist of either a single sash or two sashes, and are referred to, respectively, as single or double hung windows. A window assembly generally includes a window frame, at least one sash, a pair of opposing window jambs, each jamb having a channel for allowing the vertical travel of each sash, and usually a balance to assist with the raising and lowering of the sash to which it is attached by providing a counterbalance force to the weight of the sash.
The jambs are vertically positioned on either side of the sash within the window frame assembly. Because they must provide a space to permit the sash shoe or carrier to freely traverse up and down, and the jamb channels are not well sealed at either their top or bottom. The vertically positioned channel forms, in effect, a “chimney” that permits air to easily flow upwardly compromising the insulating value of the window. Further, dust or other fine particles can enter the jamb channel, which can ultimately gum up the carrier or at least increase the force necessary to move the carrier through the channel.
In a conventional curl spring carrier, such as is disclosed in U.S. Pat. Nos. 5,353,548 and 5,463,793, the end of the spring is attached to the wall of the jamb channel via a fastener, most commonly a screw. As the sash is manually moved to either open or close the window, the curl spring, which may be coiled up within the carrier, will either uncoil as the carrier is moved away from the point of attachment or it will retract and recoil itself within the carrier as the carrier is moved toward the point of attachment. The opening of a window will depend on the position of the sash. An upper sash will open by being moved downwardly in the jamb channel and the lower sash will be moved upwardly along the jamb channel. The points of attachment and whether the curl spring is coiled within the carrier or is uncoiled in the sash's “closed” position may vary from window design to window design.
Windows are subjected to manufacturing standards that mandate specific air flow through standards for each design. For example, there are a number of different standards which apply depending upon which region of the country the window is scheduled to be installed. A blower is sealably attached to the window by a common duct, usually by cutting a hole into the glass or plexiglass pane of one of the sashes. Pressurized air is then blown through the duct and any leaks are sought out and recorded. The minimum standard which all windows must pass is 25 miles per hour (mph). Higher pressures must be withstood by windows being installed in different parts of the country. For example, a DP (Design Pressure) of 35 is required for non-coastal applications. DP 35 is the equivalent of approximately 143 mph. DP55 is the preferred rating for coastal applications, due to higher wind pressures. DP 55 approximates to 180 mph. As is quite evident, not only must the sash panes be able to structurally withstand this high pressure, but the various moving and interacting elements of each window frame must be built to such tolerances so as to withstand or at least minimize the effects of these wind pressure standards.
Numerous attempts have been made to try to meet these aggressive standards; however they have all met with only limited success. For example, even if the window holds up to the pressure, the amount of air passing through the jamb channels via a “chimney effect” can be excessive. Attempts to block or alleviate these aerodynamic forces often cause unwanted side-effects, such as added excessive pressure to the movement of the sash, etc. What is necessary is an air block that substantially achieves the goal of minimizing air flow through the jamb channel, which also has the ancillary benefit of substantially reducing the amount of dirt particles that might accumulate within the channel, while still allowing the essentially unimpeded movement of the sash through the jamb channel. Further, the block cannot be so obtrusive so as to negatively affect the vertical travel of the sash through the jamb channel.